1-Preheat oven to 350 F: Preheat oven to 350 F. Grease 13×9 baking dish with unsalted butter and dust with flour, then set aside.
2-Prepare the cake mix according to package: Prepare the cake mix according to package directions, then mix in 2 Tablespoons lemon juice. Pour the batter into the prepared baking dish and set aside.
3-Beat 32 oz: Beat 32 oz. ricotta, lemon zest and 4 oz. mascarpone with an electric mixer on medium-low speed until smooth. Add ¾ cup sugar and vanilla, and beat until smooth. Add the eggs, one at a time, beating after each addition until just combined. Gently spread the ricotta mixture evenly over the cake batter, but do not go all the way to the edges with ricotta mixture (leave about ½ inch rim). Ricotta and cake layers will switch places during the baking.
4-Bake about 50- 60 minutes or until: Bake about 50- 60 minutes or until a wooden pick inserted in the center of the cake comes out clean. Let the cake cool completely before adding the frosting.
5-To make the frosting, beat 12 oz: To make the frosting, beat 12 oz. mascarpone with electric mixer on medium speed until smooth. Gradually add the milk, beating until smooth. Add the pudding mix and beat until smooth. Taste the frosting and if it is not sweet enough to your taste, add powdered sugar a Tablespoons at the time until reach desired sweetness. Spread frosting over the cooled cake.
6-Store the cake in the fridge: Store the cake in the fridge.